Find differential equation via Laplace transform xy′′+(2x+3)y′+(x+3)y=3e^(−x)

MMDCCC50m

MMDCCC50m

Answered question

2022-11-07

Find differential equation via Laplace transform x y + ( 2 x + 3 ) y + ( x + 3 ) y = 3 e x

Answer & Explanation

Samuel Hooper

Samuel Hooper

Beginner2022-11-08Added 15 answers

Consider the equation
t y + ( 2 t + 3 ) y + ( t + 3 ) y = a e t
then by the standard Laplace transform this becomes
s ( s 2 y ¯ ) + y ( 0 ) 2 s ( s y ¯ ) + 3 s y ¯ 3 y ( 0 ) y ¯ + 3 y ¯ = a s + 1
( s + 1 ) 2 y ¯ + ( s + 1 ) y ¯ = a s + 1 + 2 y ( 0 ) y ¯ 1 s + 1 y ¯ = a ( s + 1 ) 3 2 y ( 0 ) ( s + 1 ) 2 d d s ( y ¯ s + 1 ) = a 3 d d s ( 1 ( s + 1 ) 3 ) + 2 y ( 0 ) d d s ( 1 ( s + 1 ) 2 ) y ¯ s + 1 = a 3 1 ( s + 1 ) 3 + 2 y ( 0 ) 1 ( s + 1 ) 2 + c 0 y ¯ = a 3 1 ( s + 1 ) 2 + 2 y ( 0 ) s + 1 + c 0 ( s + 1 ) .
Inversion of the transform leads to
y ( t ) = a 3 t e t + 2 y ( 0 ) e t + c 0 ( δ ( t ) + δ ( t ) )
For this case supposing y(0)=0, a=3, and since c0 is arbitrary, or that other conditions apply, then
y ( t ) = t e t .

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